US6295813B1 - Press driven tool actuator module - Google Patents

Abstract

For a hydraulically actuated device a hydraulic power cylinder with an actuator slidably received for reciprocation within the cylinder and a piston slidably received for reciprocation within a sleeve of the actuator and defining a gas chamber on one side of the piston and a hydraulic fluid chamber on the other side of the piston so that the maximum pressure in the hydraulic fluid chamber is limited as a function of the force of compressed gas in the gas chamber acting on the piston. In this way, the maximum system pressure is a function of and substantially corresponds to the pressure of the compressed gas within the gas chamber and acting on the piston. Desirably, the pressure of the compressed gas in the gas chamber can be readily changed to change the maximum hydraulic fluid pressure.

Description

REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending application Ser. No. 08/976,775 filed Nov. 24, 1997 entitled Press Driven Tool Actuator Module.

FIELD OF THE INVENTION

This invention relates generally to fluid actuated cylinders and more particularly to an actuator for fluid actuated cylinders.

BACKGROUND OF THE INVENTION

Press driven tool modules utilizing fluid actuated cylinders have found acceptance due to their adaptability to conventional presses wherein a vertical force input by a press ram to one fluid power cylinder actuates a second fluid work cylinder to provide a horizontal or otherwise directed force output to actuate a tool to form a portion of a workpiece inclined to the axis of the press ram. This design is flexible in that various tool modules can be used with the same press to provided a number of forming operations actuated by a single press. One such press driven fluid actuated tool module is disclosed in U.S. Pat. No. 5,606,910. In this system a press ram displaces a piston of a hydraulic power cylinder to pressurize the hydraulic fluid and thereby displace a piston of a work cylinder which has a tool mounted thereon to engage the tool with the workpiece. The power cylinder has an upper reservoir containing a reserve supply of hydraulic fluid which when the piston is retracted communicates with a lower portion of the cylinder, which contains the hydraulic fluid to be pressurized by displacement of the piston, after it engages with a high pressure seal to prohibit pressurized fluid from flowing into the upper reservoir. The power cylinder must be disposed in substantially vertically upright position to function properly. When the high pressure seal wears, there is, at the very least, a loss in pressure of the hydraulic fluid when the work cylinder piston is displaced which reduces the efficiency of the system and effects the performance of the work tool in use. Further, wear on the seal can lead to failure of the power cylinder requiring replacement of the entire power cylinder or at least the high pressure seal resulting in increased down time for the system.

SUMMARY OF THE INVENTION

For a hydraulically actuated device a hydraulic power cylinder with an actuator slidably received for reciprocation within the cylinder and a piston slidably received for reciprocation within the actuator and defining in part a gas chamber on one side of the piston and a hydraulic fluid chamber on the other side of the piston so that the maximum pressure in the hydraulic fluid chamber is limited as a function of the pressure of gas in the gas chamber acting on the piston. In this way, the maximum system pressure corresponds to the pressure of the gas within the gas chamber acting on the piston. Desirably, the pressure within the gas chamber can be readily changed to change the maximum hydraulic fluid pressure.

In one form, the hydraulic actuator is used to drive a work cylinder having a work tool to form a workpiece adjacent the work cylinder. Preferably, a press displaces the actuator to decrease the volume of the hydraulic chamber and force hydraulic fluid under pressure from the hydraulic actuator to the work cylinder to drive a piston and rod of the work cylinder to displace the associated work tool to form the workpiece. A biasing member in the work cylinder acting on its rod and piston returns the hydraulic actuator to its unloaded position when the press ram is retracted from the actuator. The biasing member may be one or more gas springs carried by the work cylinder.

Objects, features and advantages of this invention include providing a hydraulic actuator which limits the maximum pressure within the hydraulic actuator and within a device driven by the hydraulic actuator, is readily adaptable to many hydraulic cylinder applications, enables the maximum hydraulic fluid pressure to be readily varied, improves the in-service useful life of the high pressure seals, is reliable durable, of relatively simple design and economical manufacture, and has a long useful life in service.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of this invention will be apparent from the following detailed description of the preferred embodiment and best mode, appended claims and accompanying drawings in which:

FIG. 1 is a sectional view of a work cylinder and a hydraulic actuator according to the invention;

FIG. 2 is a sectional view of the hydraulic actuator of FIG. 1;

FIG. 3 is a sectional view of the work cylinder of FIG. 1;

FIG. 4 is a sectional view taken along line4—4 of FIG. 3;

FIG. 5 is an end view of the work cylinder; and

FIG. 6 is a sectional view taken alongline6—6 of FIG.3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring in more detail to the drawings, FIG. 1 illustrates a hydraulic actuator10 for a hydraulically drivenwork tool12 and having anactuator14 displaceable by aram16 of apress17 to pressurize hydraulic fluid in the actuator10 and deliver it to a work cylinder18 to drive awork cylinder piston20 to advance thework tool12 along its axis to punch a hole in or form aworkpiece22 received on acarrier24. After the forming operation is complete, thepress ram16 is retracted or withdrawn and theactuator14 is returned to its retracted position by a biasing means, such as a spring or a gas spring carried by the work cylinder18 and constructed and arranged to cause thework cylinder piston20 to return it to its retracted position and displace the hydraulic fluid back into the actuator10 thereby displacing theactuator14 to its retracted position. With the system reset in its starting position, a subsequent cycle of the hydraulic actuator10 and thework tool12 can be performed to form anotherworkpiece22.

As best shown in FIGS. 1 and 2, the hydraulic actuator10 has acylinder body30 with a stepped, generallycylindrical bore32 in which theactuator14 is slidably received for reciprocation between advanced and retracted positions. Anannular bearing retainer34 is threadably received in thebore32 and has a firstannular groove36 in which anannular bearing38 is received and a secondannular groove40 in which aseal ring42 is received. Awiper44 may also be carried by theretainer34. Anoutlet46 through thecylinder body30 communicates ahydraulic fluid chamber48 with the work cylinder18. Anopening50 through thecylinder body30 may be used to add hydraulic fluid to or remove hydraulic fluid from thechamber48 and in use is closed by aplug52.

Theactuator14 has acylindrical sleeve54 threadably attached to anannular retainer56 with one or moreset screws58 received through openings in theretainer56 to fix its position relative to thesleeve54. Acap62 closes the upper end of thesleeve54 and is preferably welded or otherwise attached and sealed to thesleeve54 and preferably has agas filler valve64 extending therethrough to permit pressurized gas to be added to or removed from a gas chamber66. The gas chamber66 is defined in part by apiston68 slidably received within thesleeve54 and retained therein by an inwardly extendingedge70 of theretainer56. Thepiston68 has a firstannular groove72 which receives anannular bearing74 and a secondannular groove76 which receives aseal ring78 to prevent fluid transfer between the gas chamber66 and thehydraulic fluid chamber48. The movement of theactuator14 toward its retracted position is limited by engagement of anoverhanging edge80 of theretainer56 with an end or inwardly extendingrim82 of thebearing retainer34.

As best shown in FIGS. 1 and 3, the work cylinder18 has abody84 constructed to be bolted to a base throughmounting holes86 extending throughfeet88 of thebody84. Thebody84 has a generallycylindrical bore90 in which apiston rod92 is slidably received for reciprocation and acounterbore94 providing ashoulder96 engageable by thepiston20 which is operably connected to thepiston rod92 to limit the travel of thepiston20 androd92.

Thepiston20 preferably comprises a split ring having a throughbore and a counterbore providing arib98 received in anannular groove100 in the end of thepiston rod92. Thepiston20 is slidably received in a generally cylindrically bore of a cup shapedend cap102 threadably received in thecounterbore94 of thebody84. Thepiston20 preferably carries anannular bearing104 which guides thepiston20 for reciprocation within theend cap102. Ahydraulic fluid chamber106 is defined between thepiston20 andend cap102 and communicates with thehydraulic fluid chamber48 of the hydraulic actuator10 through anopening108 in theend cap102 and an interconnecting conduit110.

Thework cylinder body84 carries one or moreannular seals112 which prevent any fluid in achamber114 defined between thepiston rod92 and thebody84 from leaking out of the body. Any air or gas in thechamber114 may be communicated with the atmosphere through a small bleed hole (not shown) which is normally closed.

Aguide plate120 is fixed to the end of the piston rod extending from thebody84 by a pair of cap screws122 (FIG. 4) threaded into thepiston rod92. To guide thepiston rod92 for reciprocation, a pair of generallycylindrical rods124 are connected to theguide plate120 bycap screws125 threadably received in therods124 and are slidably received inbushings127 throughbores126 in thebody84. Thework tool12 is preferably threadably received in alignedopenings128,130 in theguide plate120 andpiston rod92 for comovement in unison therewith.

To yieldably bias therod92 andpiston20, as best shown in FIG. 6,gas springs132 are each received inseparate pockets134 in thebody84 and fixed therein by acap screw136 received in a threaded bore in anend cap138 of eachgas spring132. Eachgas spring132 has aplunger140 extending out of itspocket134 and engageable with abar142 connected to eachleg124 by acap screw144 to yieldably bias thebar142 and hence, theguide plate120,piston rod92 andpiston20 to their retracted positions to minimize the volume of thehydraulic fluid chamber106 to return the hydraulic fluid to the hydraulic actuator10 when theactuator14 is not engaged by thepress ram16. Thegas springs132 may be of substantially any type, such as that disclosed in U.S. Pat. No. 5,303,906, the disclosure of which is incorporated herein by reference in its entirety. Optionally, some other biasing mechanism, such as a coil spring or other mechanical device, may be provided in the pockets to yieldably bias thebar142 and connected components.

OPERATION

In use, thepress ram16 is advanced to move theactuator14 from its retracted position to its advanced position to displace the hydraulic fluid from thechamber48 of the hydraulic actuator10 to thechamber106 of the work cylinder18. The hydraulic fluid in thework cylinder chamber106 displaces thepiston20 to axially advance thework tool12. As thepiston20 is advanced, theguide plate120 is moved away from thebody84 and thebar142 is moved toward thebody84 and thus bears on and displaces theplungers140 of the gas springs132 thereby increasing the pressure of the gas in the gas springs132. As thepress ram16 is retracted, theplungers140 of the gas springs132 displace thebar142 which, through therods124, displaces theguide plate120 and hence, therod92 andpiston20 to decrease the volume of the hydraulicfluid chamber106 to return hydraulic fluid from the work cylinder18 to the hydraulic actuator10. This resets theactuator14 to its retracted position so that the system is ready for a subsequent cycle.

Thepiston68 of the hydraulic actuator10 is acted on by hydraulic fluid in thechamber48 on one face and gas in the gas chamber66 on its other face. Desirably, this permits the system operating pressure to be controlled according to the pressure of the gas in the gas chamber66. Should the force of the hydraulic fluid acting on the lower face of thepiston68 exceed the force of the gas acting on the upper face of thepiston68, thepiston68 will be slidably displaced within thesleeve54 thereby relatively increasing the volume of thehydraulic fluid chamber48 to limit the pressure therein. In one embodiment, the gas chamber66 may contain a compressed gas, such as nitrogen, at a pressure of 10 to 200 bars (150 to 3000 psi) or more. While the pressure in the gas chamber66 may increase slightly as thepiston68 is displaced, the system pressure will still be controlled as a function of the gas chamber pressure. In this way, the system operating pressure can be controlled as a direct function of the pressure of the gas in the gas chamber66. Desirably, the gas chamber pressure can be readily changed as desired for a particular application.

As an alternative, another biasing member, such as a spring, may be provided in chamber66 and acting on thepiston68. A compression coil spring or belleville spring washers may be utilized. The force of the spring would set the maximum hydraulic fluid pressure in the same manner as the compressed gas described earlier would.

Claims (14)

What is claimed is:

1. A hydraulic actuator for at least one hydraulically powered device comprising:

a hydraulic cylinder having a body with a cylindrical bore formed in the body and at least one outlet passage constructed to communicate with a hydraulically powered device;

an actuator sleeve closed at one end and slidably received for reciprocation within the bore of the body between retracted and advanced positions, a piston slidably carried by the sleeve to permit movement between a first position spaced from the closed end of the sleeve and a second position adjacent to the closed end of the sleeve, the piston being yieldably biased towards it first position, a stop carried by the body to retain the actuator sleeve in the body when the actuator sleeve is in its retracted position; and

a hydraulic chamber defined between the body and the piston, constructed to contain a hydraulic fluid therein and communicating with the outlet passage whereby when the actuator is moved toward its advanced position, the hydraulic fluid in the hydraulic chamber acts on the piston against its bias and may displace the piston relative to the actuator to thereby limit, at least until the piston reaches its second position, the maximum pressure within the hydraulic chamber.

2. The actuator of claim1 which also comprises a gas chamber defined between the piston and the sleeve and constructed to receive a pressurized gas to yieldably bias the piston to its first position.

3. The actuator of claim2 wherein the pressure of gas within the gas chamber is between 10 and 200 bars.

4. The actuator of claim1 which also comprises a retainer carried by the sleeve and having a rim engageable with the piston to retain the piston at least partially within the sleeve.

5. The actuator of claim2 wherein the retainer and sleeve have mating threads to connect the retainer to the sleeve.

6. The actuator of claim1 which also comprises a second retainer carried by the body and having a stop to retain the piston at least partially within the body.

7. The actuator of claim6 which also comprises a retainer carried by the sleeve and engageable with the stop to retain the piston at least partially within the body.

8. The actuator of claim1 which also comprises:

a body having a generally cylindrical bore and a stop;

a second piston slidably received for reciprocation within the bore between first and second positions, defining in part a fluid chamber constructed to receive a fluid under pressure from the actuator and engageable with the stop to limit movement of the second piston relative to the body;

a guide plate operably connected to the second piston and yieldably biased to move the second piston to its first position whereby, the second piston is acted on by pressurized fluid in the fluid chamber to move the second piston from its first position to its second position and by the biasing force on the guide plate to move the second piston from its second position to its first position when the biasing force is greater than the force of the fluid in the fluid chamber acting on the second piston.

9. The device of claim8 which also comprises at least one leg operably connected to the guide plate at one end and to a bar at its other end with said biasing force applied to the bar.

10. The device of claim9 which also comprises at least one gas spring carried by the body and having a plunger movable between extended and retracted positions, yieldably biased to its extended position and engageable with the bar at least when the second piston is adjacent its second position.

11. The device of claim9 which also comprises a piston rod slidably received in the body and interconnecting the second piston and the guide plate.

12. A hydraulically powered device, comprising:

a body having a generally cylindrical bore and a stop;

a piston slidably received for reciprocation within the bore between first and second positions, defining in part a fluid chamber constructed to receive a fluid under pressure and engageable with the stop to limit movement of the piston relative to the body;

a guide plate operably connected to the piston and yieldably biased to move the piston to its first position; and

at least one rod operably connected to the guide plate at one end and to a bar at its other end with said biasing force applied to the bar,

whereby, the piston is acted on by pressurized fluid in the fluid chamber to move the piston from its first position to its second position and by the biasing force on the guide plate to move the piston from its second position to its first position when the biasing force is greater than the force of the fluid in the fluid chamber acting on the piston.

13. The device of claim12 which also comprises at least one gas spring carried by the body and having a plunger movable between extended and retracted positions, yieldably biased to its extended position and engageable with the bar at least when the piston is adjacent its second position.

14. The device of claim12 which also comprises a piston rod slidably received in the body and interconnecting the piston and the guide plate.

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